None of my aquariums have substrate in them. I've had a lot of people tell me you need substrate to hold beneficial bacteria but I've never had water issues not using any substrate in any of my aquariums. I just put the Fluval FX6 cannister filter on the 125 gallon aquarium about a month ago. Before the FX6 I was running 2 Magnum 350 cannister filters along with the Fluval U4 and the sponges. I just removed one of the Marineland Magnum 350 filters today from the 125 gallon tank and I'm using it on the 55 gallon aquarium now. I run ceramic rings in the media baskets on the Magnum 350 filters and no carbon.

The 125 gallon aquarium is stocked heavy with mostly OB Peacock Cichlids and other Peacock Cichlid species along with 3 or 4 Bristlenose Pleco's.
The 55 gallon aquarium only has 2 Bristlenose in it right now but I'll be adding some African Cichlids in another week or so.
I mainly use the two 20 gallon aquariums for breeding the 5 gallon aquarium has about 15-20 OB Peacock babies in it that are about a month old now.